If like me you come from a mixed family, meaning there are conservative Republicans and liberal Democrats boisterously hashing out their differences at the holiday table, you'll have an easy time recognizing the Wyeth clan gathered to celebrate Christmas at the family's Palm Springs compound in Jon Robin Baitz's grippingly entertaining "Other Desert Cities."

The play, which opened Sunday at the Mark Taper Forum, invites us to eavesdrop on the hostilities that can't help breaking out even though the occasion is festive and everyone is supposed to be on his or her best behavior. Daughter Brooke (a superb Robin Weigert) has flown in from New York, where she has been holed up in a cottage on eastern Long Island for the last several years recovering from suicidal depression.

But political differences are a scab itching to be picked in "Other Desert Cities," which is set in 2004, shortly after George W. Bush's reelection. The justification for the Iraq war is a hot topic — one that Brooke, a liberal Democrat, and her right-wing parents, Polly (JoBeth Williams) and Lyman (Robert Foxworth), should avoid at all costs.

This won't be easy, however, with Silda (Jeannie Berlin), Polly's lefty sister and former screenwriting partner just released from alcohol rehab, baiting everyone with partisan wisecracks. When Polly asserts, "The only way to get someone not to be an invalid is to refuse to treat them as such," Silda fires back, "And there it is, folks: the entire GOP platform in a nutshell."

Trip (Michael Weston), Brooke's TV producer brother, warns that if they start talking politics this early in the day it will "just dissolve into stiff upper-lip thermonuclear family war." He's still holding out hope for a cozy family holiday, but his sister has an unsettling Christmas present for her parents: the manuscript of a memoir she has written dealing with tragic events they have worked tirelessly to cover up.

Merry Christmas, Mom and Dad: The New Yorker will be publishing an excerpt recounting the darkest and most shameful episode of your lives.

The dead in drama never seem to stay put in their graves. Ghosts, those chain-rattling reminders of the unresolved past, are restless creatures, and there's one in particular that's been hounding the Wyeths. Henry, Polly and Lyman's eldest son, committed suicide after his criminal involvement with an antiwar revolutionary group that almost cost Lyman, a B-movie actor turned Republican frontman, his lucrative standing in the party until Polly appealed to her friend (and mirror image) Nancy Reagan.

Ibsen is the master of disinterring buried secrets in the theater. Baitz isn't quite as effective at steadily applying dramatic pressure to force those repressed truths into the light. The plot of "Other Desert Cities" pulls a fast one on its audience in a manner that isn't always psychologically credible. But there's no denying the intelligent and utterly timely vision behind the play.

Renowned for his scintillating wit, Baitz employs comedy not just to make us laugh but to get us to rethink our assumptions about morality. In plays such as "The Substance of Fire" (which also revolves around a family battle over a manuscript) and "A Fair Country," he purposely makes it difficult to pinpoint the exact source of corruption. In a broken world, one can't afford to be schematic about good and evil. Yet the characters of "Other Desert Cities," particularly the women, are supremely confident in the rightness of their positions.

The showdown between Polly, fierce protector of her family's privacy, and Brooke, determined truth-teller no longer able to countenance the sickly status quo, is meant to serve as a microcosm of a divided America in which reality is viewed through the lens of one's preconceived beliefs.

The maturity of "Other Desert Cities" (for my money, Baitz's best play) stems from the playwright's acceptance of the fact that human beings — limited by their own perspective, confounded by the perspective of others — are stuck with each other. "We must love one another or die," says W.H. Auden, a sentiment Baitz ratifies here.

The Taper production, directed by Robert Egan, seems determined not to let the comedy overtake the drama. When I first saw the play at Lincoln Center, I was dazzled by the comic brio of Stockard Channing, who played Polly as a Chanel-wearing general of country club wars, and Linda Lavin, who had the audience in hysterics before even one of Silda's zingers fully passed her lips.

Williams' Polly isn't quite as formidable — she needn't be a monster, but her guns aren't as blazing as they should be. Berlin's Silda has the funniest lines, but her warped delivery slows down the play's velocity.

The uncertain rhythm of Egan's staging isn't helped by a living room set by Takeshi Kata that makes the affluent Wyeths look like they decorated on the cheap. In this less glamorous setting, the repartee loses its snap, and the play's exposition seems lumpier.

But there's an upside to the production's diminished zest: the Wyeths come off like an actual family. The scenes between Brooke and Trip have a tender familiarity. And the affection between Brooke and Lyman is palpable, never more painfully so than when they are at loggerheads over the book.

Weston wonderfully embodies Trip's essential contradiction — that he is an outwardly happy character who is as inwardly challenged as any of us. And Foxworth turns Lyman into an old lion — he might not have much heart left for fighting, but he is too loyal to abandon his wife when she's on the warpath

Weigert's delicately modulated performance is the soul of the production. She so lucidly reads the emotional through line of the play that she makes even those points where the thread gets broken seem whole and natural.

Brooke isn't an easy character to play. There are all the clichés about nervous breakdowns that have to be avoided. The line she walks between stridency and self-assertion is fuzzy. And the playwright redirects her journey rather abruptly in the climactic scene, introducing information that raises more questions than answers.

Yet in finding the truth moment to moment in the puzzle that is her life, Weigert's Brooke reveals the larger truth of Baitz's wise and compassionate play.

Justin Long has withdrawn from the upcoming Los Angeles premiere of "Other Desert Cities" at the Mark Taper Forum, which is set to begin performances on Nov. 28. Center Theatre Group said that the actor had to leave the play due to "a film commitment."

The Los Angeles premiere of "Other Desert Cities" by Jon Robin Baitz is to feature Jeannie Berlin, JoBeth Williams and Robin Weigert. The actors are joining the previously announced Justin Long and Robert Foxworth in the comedy about a wealthy family living in Palm Springs.

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